Bull Sharks in Mozambique with Lukas Mueller
Lukas Mueller grew up in a small inland coal-mining town in Germany, but developed a love of freediving as part of The Watermen Project, where he used his breath-hold skills to work with large predatory sharks. He is now a PhD candidate at Wageningen University in the Netherlands and a project leader within MMF, developing a bull shark research program in Mozambique. Lukas has recently been in the field for several weeks, so I talked to him while he was in home self-isolation back in Germany. SJP
How did the project begin?
I was fortunate to meet Dr. Andrea Marshall in Indonesia while she was doing research. We joined her to work on a virtual reality film about manta rays. We kept in touch afterwards, and in 2018 she asked if I'd like to join in on some bull shark research in Mozambique. I packed my bags and was in Mozambique a couple of weeks later!
That was my first introduction to the Bazaruto Seascape. It's like two worlds intertwined: and a huge lagoon-like habitat, crisscrossed by sandbanks, that extends from the coast to the outer islands, and an oceanic ecosystem offshore. Three major islands form the Bazaruto Archipelago, and they act as a barrier to separate this lagoon system from the open ocean. Tidal movement creates a cyclical system of water exchange, pushing ocean water into the lagoon, then pulling the warm water across the offshore reefs on the outgoing tide.
That regular movement of nutrients and animals between the habitats makes the whole area super productive, but the dynamics are complicated. Andrea has been diving around Bazaruto since 2006, so she already had a sighting and photo-identification dataset for bull sharks from her research dives. She and Janneman Conradie know the area really well, so they had a good idea of where and when the bull sharks were most likely to be seen in different conditions. If I'd been working by myself as a PhD student, I'd have had no chance.
Science with bite
I'd worked with bull sharks before, in places like the Bahamas, Florida, and Mexico, but the behavior of the sharks in Mozambique is very different to that I'd seen elsewhere. I'm used to them being confident and inquisitive. In Mozambique, they're extremely shy, unless there's action in the water; spearfishing, for instance. In that situation, they might give you a full charge, in bad visibility. I'd been planning to place tags on them while I was freediving, but that situation didn’t make 35–40 m dives too inviting.
Free-tagging the sharks was not the only option, though. There are various methods available, such as using a pole to tag the shark near the surface, or catching the shark to implant a tag, or attaching a tag to the fin using a clamp or harness. Working through the options, we realized that catching the sharks would be best, but most of MMFs previous research work has used non-invasive in-water techniques. We decided to ask for help.
Fortunately, there's a whole crew of amazing shark scientists and fishermen working in the south of Mozambique, at Ponta do Ouro, that have experience with bull shark research in similar conditions. That's kicked off a big adventure over the past two years through collaboration with Dr. Ryan Daly and his team. Ryan had tagged over 100 bull sharks already, some of which swam all the way up the coast to Bazaruto, so it was great to be able to combine the tagging experience of the Ponta do Ouro team with Andrea and Janneman's knowledge of the Bazaruto Seascape.
When we tag these animals we think first about the shark's welfare, but we have to consider our own welfare too. These sharks, they're big, they're powerful, they're several hundred kilograms of apex predator. And we're working off an inflatable boat! There's a unique focus when you work with an animal like that. We use a 2 cm-thick protective belt over the pontoons. Once the shark is hooked, we get it to the boat as fast as possible, then we flip it onto its back in the water so it goes into a trance-like state known as tonic immobility. While that’s going on, there's a person whose only job is to manage the line coming into the boat, making sure that no feet, toes, hands, or legs get wrapped; otherwise, if the shark decides to make another last run, you're going with it. Once the shark is next to the boat, the shark will try to bite and kick its tail. We've been hit by tails a couple of times now, and the bruises last for weeks. These sharks will absolutely batter you.
Once the shark is secure, we use a sterile surgical kit to make a small incision into the shark's body cavity, then insert one of our acoustic tags. We’ve set these tags to transmit an ultrasonic ping for the next 10 years. Then, we also attach a small satellite tag in the dorsal fin with some surgical tubing. None of this leads to any long-term harm or consequences for the shark. Over the 100+ sharks that Ryan has tagged, they've never had any mortalities or evidence of damage, and they still regularly see those sharks while diving now, 4–5 years after the start of their project. All of our sharks have been doing well too – we've been receiving lots of pings!
Bull sharks in Bazaruto
We can detect the tagged sharks by deploying bottle-sized acoustic receivers, we call them 'listening stations', on reefs within and around the Bazaruto Seascape. Andrea pulled up the stations for download while I was stuck in lockdown here in Germany, and it's given us some great insights into what the sharks are up to. These bull sharks are highly resident. Extremely resident in some cases. One shark, tagged over 18 months ago, has been detected at one specific reef almost every day since. The Seascape area is a key habitat for these bull sharks.
'Our' sharks, though, weren't the only ones that we recorded. We also received pings from some of the bull sharks that Ryan had tagged down in Ponta do Ouro. We're continuing to expand our receiver array, so it's going to be really interesting to see how much connectivity there is between the sharks in Bazaruto, Ponta do Ouro, and South Africa. It's becoming evident that the sharks are sometimes traveling thousands of kilometers along this coast.
All of the bull sharks that we've captured in Bazaruto have been adult females but, down in Ponta do Ouro, Ryan sees a 50/50 split between females and males. Further south again, in South Africa, the bull sharks are mostly males. It might be that the females are staying up here, around these protected reefs where they have plenty to eat, while the males are migrating over large distances. Ryan is looking into that using his larger dataset. But it shows that it's often not as simple as 'migratory' and 'resident' animals, as there can be quite complex movement patterns going on within a species.
It's very encouraging for us to see that some of the hotspots for the sharks, especially these adult females, are inside protected areas within the Bazaruto Seascape. They're more exposed when they leave this area, which speaks to the need for a network of protected reef systems and a joint conservation strategy between Mozambique and South Africa. Obviously, it's unrealistic for us to try to protect this whole coastline and, anyway, sustainable fishing is a vital source of livelihoods and food. Bull sharks are a critical part of this ecosystem though, they're the apex predator along this coast, and we can ensure that key reefs are well-maintained so that these migratory individuals can stop and replenish on long journeys. It's not just the bull sharks, it's also the manta rays, whale sharks, and a host of other species that are also migrating along this coast, so it’s great that the work MMF is doing is helping to create this cohesive plan.
This is an amazing project to be a part of. We’ve done all this exploration, been bashed up by sharks, and dedicated so much time and funding towards this work; it's really difficult at times. We've all been working so hard to get this information. And then, we download that first acoustic receiver station and see the data, and wow, it’s insane. And knowing that we're going to keep getting more data over the next 10 years, a light bulb goes on in my brain because, holy moly, this is a game-changer. If we can tag 20–25 animals like this, the data that we're going to collect is going to tell us so much about the sharks, and how we can best protect this whole ecosystem.
Conservation flagships
Andrea calls this area the 'Marine Serengeti'. That got me thinking, why did first want to protect these amazing terrestrial ecosystems that are so famous and iconic now? Was it because of the termites and butterflies, which are very cool animals in themselves? No, it was because of the megafauna, it was the lions and the rhinos and all the other animals we read about as kids. And that's where the Marine Megafauna Foundation's strategy really resonates with me. People are so often drawn towards the ocean by whales, sharks, sea turtles, and other charismatic animals. These big, well-known animals serve as an emotional hook that engages people. By protecting these species, and their habitats, we're also protecting so many other animals; even species we don't even know about yet. That's how I think about it. We see the most conservation success globally by harnessing the public appreciation for these flagship species to unlock broader-scale habitat protection. And that's what I see when I look around the MMF team where, through research and conservation work, we're protecting these endangered species and their habitats. That's why I'm so passionate about the work we're doing.
If you look at a global map of marine protected areas, less than 5% of the ocean is fully protected. And outside these areas, it's often a free-for-all. One experience that really changed me was joining Janneman on an expedition up to the north of Mozambique. It was shocking to see hundreds of kilometers of coastline being fished out, sand mines, and other resource extraction happening, destroying habitats as we watched. But we can protect marine habitats while supporting people, too. I used to do a lot of expeditions where you touched down near the harbor, you got on the research vessel, you went out for two weeks, you did your job, you came back with results, and you left again. In Mozambique, I've been living in the community, and I'm starting to understand the culture better. For people like me, that grew up far from the ocean, there's still this emotional connection that draws us to the coast, often some formative experience that connects us to these marine animals. Here in Mozambique, though, if the marine ecosystem is degraded, people are also losing the foundation of their livelihood. The ocean offers a whole range of resources, as well as food, that allows the manufacture of other products. It was all working okay, too, before foreign powers started using Mozambique as a pawn in their geopolitical games, and international fishing fleets from Europe and elsewhere came in to exploit the resources they'd wiped out in their own seas. If the fisheries here disappear or degrade because we've let these ecosystems die, that will have massive ramifications for everyone. It makes sense for everyone to protect some of these habitats so that the broader ecosystem can thrive. Our conservation team at MMF works through these issues with the fishers themselves, and their communities, which is why we have good conservation momentum in Mozambique, despite all the challenges.
As we improve protections, we need to put in place funding mechanisms to support the ecosystem rebuild too. The conservation space is so dramatically underfunded, but what's encouraging to me is the demand I see for doing trips with the MMF team around the world which, of course, is a big part of how we fund these programs. All of us, the people listening to or reading this, we have a special passion for these ocean animals and habitats. And whenever I see people pay for a natural experience, whether it’s joining one of our expeditions or visiting a national park, that transaction shows they're taking their money, and they're using it to invest in protecting biodiversity.
And that goes for me too. People ask me, 'Why don't you work in the Mediterranean? It's much closer to Germany. It's logistically easier. It's nice weather, you’ll get great food.” But the Mediterranean is dead. There are some areas where life is coming back, sure, and it's certainly worth investing in those. But I've got a chance here, this once-in-a-lifetime shot to help protect this amazing, pristine habitat, the Inhambane coastline, the ocean analog to the Serengeti or Kruger National Park. Given the choice between that, or trying to rebuild a dead ecosystem in the Mediterranean, then I'll always choose Mozambique. If we don't prioritize places like this, we're going to lose a lot of critical habitats around the world that we can still save. Here, I can make a big difference right now.
